Computer systems (e.g., integrated microcomputers) comprise processors (e.g., a central processing unit CPU), memory units (e.g., a random access memory RAM), busses, and other components. Interfaces exchange data and control information between these components and peripheral devices (e.g., displays, printers, buzzers). For example, the processor writes data to the memory and the interface sends this data to the peripheral device, or vice versa. To save processor resources, it is convenient to control the interface partly or completely independent from the processor.
A queued serial peripheral interface unit (QSPI) is incorporated in many microcomputers and peripherals. The following references are useful: U.S. Pat. No. 4,816,996 [1] and 4,958,277 [2], both to Hill et al., and "Queued Serial Module (QSM) Reference Manual" by Motorola, Inc. 1991, order number QSMRM/AD, hereinafter [3]. A queue is a plurality of memory entries which are consecutively retrieved from the memory or written into the memory.
Section 4 of reference [3] explains communications parameters, such as for example, serial clock baud rate SPBR, bits per transfer BITS, length of delay after transfer DTL, clock polarity CPOL, clock phase CPHA, and others. All communication parameters needed for transmitting a queue are collectively referred to as parameter set. The CPU defines the parameter set for every queue and writes the parameters of the required set to control registers. When a new queue is activated, the CPU writes a new parameter set to the control register. In other words, the parameters are associated with the queues. The software designer who designs CPU instructions has to take care for each communication parameter. This approach is cost intensive and not convenient. Also, during a queue transfer, the parameter set can not be modified. It is sometimes desirable to begin a queue transfer with a first parameter set and switch to a second parameter set. Using the QSPI described in references [1], [2] and [3] a queue transfer should be stopped and initiated again with newly loaded communication parameters.
The present invention seeks to provide a computer system with an improved interface and a method which mitigate or avoid these and other disadvantages and limitations of the prior art.